                (let [childy (actx-y (:child-actx delta))
                      ay (actx-y (:actx delta))
                      cy (ch-y (:ch delta))]
-                 [(case (:delta delta)
-                    :put (when (get chs (:ch delta))
-                           ["<g transform='translate(500," ay ")'>"
-                            "<line class='delta' x1='0' y1='0' x2='100' y2='"
-                            (- cy ay) "' stroke='green'"])
-                    :take (when (get chs (:ch delta))
-                            ["<g transform='translate(600," cy ")'>"
-                             "<line class='delta' x1='0' y1='0' x2='-100' y2='"
-                             (- ay cy) "' stroke='" (if (:msg delta) "green" "black") "'"])
-                    :actx-start (when (> childy line-height)
-                                  ["<g transform='translate(30," ay ")'>"
-                                   "<line class='delta' x1='0' y1='0' x2='30' y2='"
-                                   (- childy ay) "' stroke='green'"])
-                    :actx-end (when (> childy line-height)
-                                ["<g transform='translate(60," childy ")'>"
-                                 "<line class='delta' x1='0' y1='0' x2='-30' y2='"
-                                 (- ay childy) "' stroke='black'"])
-                    nil)
-                  " stroke-width='1' marker-end='url(#triangle)'/></g>"
-                  (when (:ch-name delta)
-                    ["<text class='ch-name' x='540' y='" (* 0.5 (+ ay cy))
-                     "'>" (:ch-name delta) "</text>"])])))
+                 (when (not= ay cy)
+                   [(case (:delta delta)
+                      :put (when (get chs (:ch delta))
+                             ["<g transform='translate(500," ay ")'>"
+                              "<line class='delta' x1='0' y1='0' x2='100' y2='"
+                              (- cy ay) "' stroke='green'"])
+                      :take (when (get chs (:ch delta))
+                              ["<g transform='translate(600," cy ")'>"
+                               "<line class='delta' x1='0' y1='0' x2='-100' y2='"
+                               (- ay cy) "' stroke='" (if (:msg delta) "green" "black") "'"])
+                      :actx-start (when (> childy line-height)
+                                    ["<g transform='translate(30," ay ")'>"
+                                     "<line class='delta' x1='0' y1='0' x2='30' y2='"
+                                     (- childy ay) "' stroke='green'"])
+                      :actx-end (when (> childy line-height)
+                                  ["<g transform='translate(60," childy ")'>"
+                                   "<line class='delta' x1='0' y1='0' x2='-30' y2='"
+                                   (- ay childy) "' stroke='black'"])
+                      nil)
+                    " stroke-width='1' marker-end='url(#triangle)'/></g>"
+                    (when (:ch-name delta)
+                      ["<text class='ch-name' x='540' y='" (* 0.5 (+ ay cy))
+                       "'>" (:ch-name delta) "</text>"])]))))
            deltas)]))
 
 ;; ------------------------------------------------

          (when (< @event-delay 0) (<! step-ch)))
        (assign-positions @vis @root-actx vis-positions actx-ch-ch-infos nil)
        (set-el-innerHTML (str el-prefix "-html")
                          (apply str (flatten (vis-html-actx @vis @root-actx
                                                             actx-ch-ch-infos false))))
        (set-el-innerHTML (str el-prefix "-svg")
                          (apply str (flatten (vis-svg-actxs @vis @vis-positions
                                                             deltas :curr))))
        (recur (inc num-events) @vis @vis-positions)))
    (ago world w
         (reset! root-actx world)

               ["<li id='ch-" ch-id "'>" ch-id ": " (:msgs ch-info) "</li>"]))
           (get actx-ch-ch-infos actx))
     "</ul></div>"
     (when (not (:closed actx-info))
       ["<ul>" (mapv (fn [child-actx]
                       ["<li>" (vis-html-actx vis child-actx actx-ch-ch-infos)
                        "</li>"])
                     (sort #(compare (last %1) (last %2)) (keys children)))
        "</ul>"])
     "</div>"]))

;; ------------------------------------------------
